As is known, blenders are used for making home-made ice-cream, and normally comprise a cylindrical, horizontal-axis bowl into which the ingredients for producing a given quantity of ice-cream are poured; a cooling unit for cooling and maintaining the bowl and contents at a temperature ranging between −10° C. and −35° C.; and a rotary mixing member mounted for rotation inside the bowl to blend the ingredients at the various ice-cream-making stages.
In addition, the mixing member is shaped to uninterruptedly scrape the whole cylindrical inner surface of the bowl, to prevent the ingredient mixture inside the bowl from adhering to the lateral wall on account of the low temperature of the lateral wall.
More specifically, most currently marketed mixing members extend coaxially with a longitudinal axis, which, in use, coincides with the axis of symmetry of the bowl, and substantially comprise a number of elongated rectangular radial blades spaced angularly about the longitudinal axis of the mixing member; and two end connecting hubs, which are coaxial with the longitudinal axis of the mixing member, are located on opposite sides of the blades, and are shaped to connect the axial ends of the blades to form a rigid structure that can rotate easily about the longitudinal axis of the mixing member.
Normally, the radial blades extend helically about the longitudinal axis of the mixing member, and are angularly spaced about the axis so that the outer lateral edges of the blades lie on a cylindrical surface of a diameter approximately equal to but no larger than the diameter of the bowl; and one of the end hubs has a supporting shaft or pin projecting from the hub body, coaxially with the longitudinal axis of the mixing member, and terminating with a splined head for connection to an electric motor inside the blender.
To scrape off the ice-cream sticking to the lateral wall of the bowl, mixing members of the type described above also comprise a number of plastic scrapers fixed to the outer lateral edges of the flat blades and movable freely in the blade planes, i.e. radially; and a number of helical push springs fitted to the blades to push the individual scrapers radially outwards, so that each rests against the cylindrical inner surface of the lateral wall of the bowl.
Though highly efficient, known mixing members have the major drawback of being relatively difficult to clean, on account of the ice-cream accumulating in the cavities housing the helical springs and scrapers, with all the obvious problems this involves.
Known mixing members also have the major drawback of performing poorly when the scrapers are called upon to remove thicker and harder than normal ice-cream off the wall surface, on account, for example, of more intense cooling of the lateral wall of the bowl. In which case, the elastic force of the helical springs may not be sufficient for the scrapers to adhere to the surface of the lateral wall of the bowl.